The present invention is directed to a subscriber-side network termination unit and method of operating some of an access line network having: (a) an interface for the access line network-side transmission and reception of a transmission frame with a plurality of data channels, including a signaling channel,: (b) an interface for the subscriber-side offering of telecommunication payload data channels for telecommunication applications as well as a signaling channel allocated to these telecommunication payload data channels; and: (c) an interface for the subscriber-side offering of data channels for data applications.
In the subscriber access area, modern telecommunication networks have digital access line networks available to them that connect one or more local switching centers to subscriber terminal equipment via subscriber line networks and subscriber-side network termination units. Access line networks were originally designed for the transmission of low-frequency information signals such as, for example, in analog telephony or in the employment of narrow band services. The bit rate transmitted at the subscriber side in the access line network is thereby defined, for example for a narrow band ISDN basic access, such that the longest subscriber lines that occur still can be used. Apart from data rates of 16 kbit/s employed for synchronization and echo suppression purposes, the narrow band ISDN basic access, which is also referred to as BA (from the English expression xe2x80x9cBasic Accessxe2x80x9d), has a data rate of 144 kbit/s divided into a control channel referred to as D-channel with 16 kbit/s and into two payload channels of 64 kbit/s each that are referred to as B-channels. As a result of this dimensioning basis, a large part of the bit rate that can be maximally dependably transmitted, i.e. of the maximum band width in the access line network area with shorter subscriber lines, remains unused. The degree of attenuation for symmetrical double leads of copper subscriber lines that limits the range of the digital signal transmission, increases with the line length. It is generally valid that the bit rate to be transmitted over a subscriber line can be all the higher the shorter the length of this subscriber line. Access line networks designed for narrow band services, consequently, are also suitable for the transmission of more broad band services. Methods have thus prevailed in recent years with which the existing copper lines in the access line network can be utilized for the transmission of digital information signals.
Vittorio Ferretti, Guillermo Wichmann, xe2x80x9cMehrfachnutzung von Teilnehmeranschlubkabelnxe2x80x9d, Telecom Report, 14 (1991), No. 3, pages 150-153 discloses a method for dividing the payload data rate of an ISDN-BA of 144 kbit/s into a control channel referred to as D-channel and, optionally, two payload channels each having 32 kbit/s and a payload channel having 64 kbit/s data rate, preferably provided for data applications, or four payload channels each having a 32 kbit/s data rate. Although the plurality of applications, terminal equipment or subscribers connectable via a line pair and a specific network termination unit is increased, the data rate that is available for an application is reduced compared to an ISDN BA or remains of the same size in the best case.
The connection of data processing equipment such as, for example, a computer or an LAN to an access line network of a communication network usually occurs for small companies or private households via a modem and a switched analog or digital connection, or via an ISDN connection having a maximally obtainable data rate of 128 kbit/s.
The patent application DE 196 25 385 3, which was not yet published as of the priority date of the present application, discloses a method for the transmission of information signals in an access line network via subscriber lines, whereby transmission parameters of the subscriber line are measured and settings are undertaken at the exchange side and at the subscriber side based on the criterion of the measured results. These settings, for example, are the bit rate that can be maximally dependably transmitted and, potentially, the transmission method. As a result thereof, bit rate and transmission method can be adaptively undertaken line-individually dependent on the physical transmission parameters. In addition to a D-channel with a band width of 16 kbit/s, it thus becomes possible to transmit even more payload channels wherein each channel has a band width of 64 kbit/s. The maximum plurality of transmittable payload channels is thereby dependent on the band width of the individual subscriber line configuration, particularly on the length of the subscriber line.
To provide an information transport frame divided into time slots of equal size is known as a method for the subscriber-side information transmission in such access line networks. Such method is known from the article by M. N. Huber and P. J. Kxc3xchn, xe2x80x9cModelling of a Multi-Queue Polling System with Arbitrary Server Interrupts for the Idle-Slot Concatenation Packet Switching Principle in a Hybrid CS/PS Nodexe2x80x9d, Proceedings of the 12th International Teletraffic Congress, Torino, 1988. Each of these time slots is occupied either with switching system data (CS data based on the English expression xe2x80x9cCircuit Switchingxe2x80x9d) or with packet data (PS data from the English expression xe2x80x9cPacket Switchingxe2x80x9d), whereby all prime slots not occupied with switching system data are combined to form a remaining packet data transport channel (idle slot concatenation). The traffic type with which the remaining packet data transport channel is occupied, for example ATM or LAN/Ethernet, is determined by the connection configuration, particularly by the packet data protocol that can be processed by the protocol evaluation means of the subscriber side.
A patent application by the same assignee that was not published as of the filing date of this application discloses a method for a subscriber-side information transmission in an access line network with the assistance of an information transport frame divided into time slots of equal size, wherein at least some of these time slots are payload channel time slots whereof each is occupied either with switching system data or with packet data and all payload channel time slots not occupied with switching system data are combined to form a remaining packet data transport channel. A protocol discriminator that enables an unambiguous allocation of the data contained in a time slot of the remaining packet data transport channel to a traffic type is inserted into every time slot of the remaining packet data transport channel, so that a protocol evaluation that is specific to a traffic type can be respectively undertaken at the reception side. This enables the utilization of the remaining packet data transport channel, which is also called ISC channel or idle slot concatenation channel, by different traffic types such as, for example, ATM and LAN. As warranted, a length particular inserted per message additionally can be communicated given messages of variable length. For the transmission of variable-length messages, another version of such a method provides that a time slot of the remaining packet data transport channel not be occupied between two messages in the remaining packet data transport channel. A time slot of the information transport frame thereby also can be used for frame control, and one time slot can be employed for ISDN signaling, wherein these time slots provided for the transmission of control information preferably are arranged at permanently defined locations within the information transport frame.
An object of the present invention, therefore is to specify a subscriber-side network termination unit of an access line network that adapts an access line network offering a plurality of payload channels to subscriber applications in order to enable a more flexible utilization of such an access line network for telecommunication applications and data applications. Moreover, a method for operating such a network termination unit also should be specified.
The present invention defines a subscriber-side network termination unit of an access line network having: (a) a first interface offered by an access line interface control for the access line network-side transmission and reception of a transmission frame containing a plurality of data channels, including a signaling channel; (b) a second interface offered by a telecommunication interface control for the subscriber-side offering of telecommunication payload data channels for telecommunication applications as well as a signaling channel allocated to these telecommunication payload data channels; and (c) a third interface offered by a data interface control for the subscriber-side offering of data channels for data applications.
An inventive method for operating such a subscriber-side network termination unit provides that, before the transmission of payload data via either the second or third interfaces, signaling data respectively allocated to the payload data are transmitted via the signaling channel of the interface offered by the telecommunication interface control.
An inventive subscriber-side network termination unit that enables the implementation of such a method, but also reflects an aspect of the present invention independently of such method, contains a control device for enabling a data transmission via the data interface control after a signaling allocated to this data transmission has occured via the signaling channel of the second interface.
As a result of the inventive method, and in the inventive, subscriber-side network termination unit, the signaling channel of the second interface is employed both as signaling channel for the telecommunication payload data channels of the second interface and as a signaling channel for the payload data channels of the third interface. This enables the simple imaging of the two subscriber-side interfaces onto a single access line network-side interface having only one signaling channel, wherein a signaling channel, namely that of the second interface, is available as needed for each of the subscriber-side interfaces. Since a signaling channel is usually required only for a brief time, namely during the signaling phase, and signaling data are unproblematical in view of delay times, one signaling channel also suffices for two interfaces.
In an embodiment of the method of the present invention, it is provided that the data interface control controls the transmission of signaling data allocated to payload data to be transmitted via the third interface via the signaling channel of the interface offered by the telecommunication interface control before these payload data are transmitted via the third interface. A control of the transmission of the signaling data provided for data of the third interface via the signaling channel of the second interface makes it possible that the data application, for example a computer or a LAN with connected computers, need access the subscriber-side network termination unit only via a single interface, namely the third interface. An alternative embodiment of such a method requires that the data application accesses the subscriber-side network termination unit via the third interface and accesses at least via the signaling channel of the second interface. The access via the second interface can thereby occur, for example, by operating the data application as communication terminal equipment at the second interface.
Another embodiment of the inventive method provides that data transmitted into the telecommunication payload data channels of the second interface at the subscriber side are only transmitted in specific data channels in the access line network-side transmission frame. As a result thereof, a fixed allocation of the payload data channels of the second interface to data channels of the transmission frame of the first interface and, thus, a simple conversion between channels of this subscriber-side interface and channels of the access line network-side interface is enabled. It is thereby preferred that the signaling channel of the second interface also is permanently allocated to either a data channel or a signaling channel of the transmission frame of the first interface.
An advantageous development of this aspect of the present invention provides that data transmitted at the subscriber side in the data channels of the third interface are preferably transmitted in the access line network-side transmission frame in free data channels not provided for the transmission of subscriber-side data transmitted in the telecommunication payload data channels of the second interface. This also enables a fixed allocation of specific data channels of the transmission frame of the first interface to the data channels of the third interface and, thus, a facilitated conversion method between these interfaces.
A consistently fixed allocation of all data channels of the third interface to data channels of the transmission frame of the first interface, however, could potentially greatly limit the band width or, respectively, data rate made available for data applications. A modified embodiment of this aspect of the present invention therefore provides that data transmitted subscriber-side in the data channels of the third interface are also transmitted in the data channels provided for the transmission of subscriber-side data transmitted in the telecommunication payload data channels of the second interface when inadequate data channels provided for the transmission of subscriber-side data transmitted in the telecommunication payload data channels of the second interface are not free in the access line network-side transmission frame for these data. When, given such a development of the present invention, adequate band width is not made available for a data application by data channels of the transmission frame of the first interface permanently allocated to the data channels of the third interface, data channels of the transmission frame of the first interface permanently allocated to the payload data channels of the second interface also are employed for the transmission of payload data of the third interface. A data channel of the transmission frame of the first interface potentially allocated to the signaling channel of the second interface is not employed for the transmission of payload data of the third interface since this signaling channel is also required for the third interface.
I an embodiment of the subscriber-side network termination unit, it is provided that the second interface offers two telecommunication payload data channels for telecommunication applications at the subscriber side. When, in particular, the two telecommunication payload data channels offered by the second interface respectively have a data rate of 64 kbit/s in a development of such an embodiment of a subscriber-side network termination unit and the signaling channel offered by the second interface has a data rate of 16 kbit/s, this interface corresponds to a standardized interface according to narrow band ISDN that is referred to as So interface.
Another embodiment of the subscriber-side network termination unit provides that the first interface offers a transmission frame at the access line network side having a plurality of data channels with a respective data rate of 64 kbit/s. The conversion of the access line network-side data channels into the payload data channels of the subscriber-side, second interface with the same transmission rate thereby can be very simply implemented and is reduced to a purely physical conversion given a fixed channel allocation.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawing.